The present invention relates to a layered film which exhibits, when used as a sealant film, excellent openability, good clouding property (the xe2x80x9ccloudingxe2x80x9d as used herein means the xe2x80x9cwhiteningxe2x80x9d), high water vapor barrier property and superior seal strength stability and which is suitable as a medical packaging material, and also relates to a packaging product thereof.
In particular, the layered film of the present invention is suitable as a sealant film for a packaging product which is produced through knurl-sealing, such as a packaging product for a blood sugar measuring electrode.
This application is based on Japanese Patent Application No. 2000-217338, Japanese Patent Application No. 2001-188658 and U.S. Provisional Patent Application No. 60/249,291, the contents of which are incorporated herein by reference.
Heretofore, polyolefin film is used as various food or medical packaging materials by making use of its characteristic features such as inexpensivenss, resistance against heat or chemicals and easy heat sealability.
In the food packaging material, an aluminum foil, a saponified product of ethylene-vinyl acetate copolymer resin and vinylidene chloride resin are used as a gas barrier layer, the gas barrier layer is combined with a polyamide resin layer, a polyester resin layer and the like, and a polyolefin-base resin such as polypropylene or polyethylene is used as a heat seal layer. Also in the medical packaging material, a polyolefin-base resin is used as a heat seal layer.
With respect to the easily openable sealant film, a method of using a resin composition obtained by mixing polypropylene and polyethylene for the sealant layer, and a method of using a resin obtained by graft-polymerizing styrene to a polyolefin-base resin are known.
In the sealant film for a packaging product which is produced through knurl-sealing, such as a packaging product for a blood sugar measuring electrode, a resin composition obtained by mixing a linear low-density polyethylene with a low melting point polypropylene has been heretofore used for the sealant layer and thereon, a homopolypropylene as a substrate layer is stacked.
The sealant film is characterized in that when the packaging product is opened, the heat sealed portion is clouded (xe2x80x9cthe heat sealed portion is cloudedxe2x80x9d as used herein means that the heat sealed portion is whitened) and therefore, it can be confirmed that the packaging product was infallibly heat-sealed.
However, the sealant film has a problem in that since the heat seal strength is as high as 1,200 g/15 mm-width or more, opening is difficult; since the latitude of the heat seal temperature is narrow, the knurl-sealing machine fails in controlling the temperature; or when the heat seal pressure fluctuates, homopolypropylenes are heat-sealed with each other and opening cannot be attained.
Examples of the easily openable sealant film include a packaging product having a heat sealable resin layer which comprises a resin composition layer having a thickness of 5 to 25 xcexcm and containing a crystalline polypropylene-base resin having a melt index of 2 to 100 (g/10 min) and a polyethylene having a melt index of 2 to 50 (g/10 min) in a weight ratio of 50:50 to 95:5 (see, JP-A-58-1672 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d)), an easily openable drop lid comprising three layers of an uppermost layer formed of a heat-resistant resin layer, an intermediate layer formed of a polypropylene and a cohesive failure sealant layer provided under the intermediate layer and formed of a polypropylene-polyethylene blend polymer (see, JP-U-B-61-37647 (the term xe2x80x9cJP-U-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese utility model publicationxe2x80x9d)), a container comprising a film layer formed of a blend material of a base resin comprising a crystalline polypropylene or a crystalline propylene-ethylene copolymer with from 8 to 30 wt % of an ethylene-vinyl acetate copolymer having a vinyl acetate content of 8 to 5 wt %, where the heat seal strength after the thermal sterilization is 100 to 1,700 g/cm (see, JP-A-57-28777), and a composite film comprising a propylene-base resin layer and a resin composition layer containing a propylene-ethylene random copolymer and/or a propylene-ethylene-butene-1 ternary copolymer, and a high-pressure polyethylene and/or a linear low-density polyethylene (see, JP-A-63-179741).
These sealant films have a problem in that the low-temperature heat sealability is inferior, the opening strength is too strong or the heat seal portion shows poor clouding or is not clouded at all at the time of opening.
Examples of the case using a combination of a polyethylene and a polybutene-1 as in the present invention include a method of blending a polyethylene and a polybutene-1 for preventing distortion and cracking of a polyethylene-made bottle, pipe, electric wire coating or the like due to contact with a viscous liquid (see, JP-B-39-22351 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means as an xe2x80x9cexamined Japanese patent publicationxe2x80x9d)). However, this publication neither discloses nor suggests the object of the present invention or the method for solving the problems described in the present invention.
The object of the present invention is to provide a layered film which exhibits excellent openability, good clouding property, high water vapor barrier property and superior seal strength stability as compared with conventional films, and which is suitable as a food or medical packaging material fitted to knurl-sealing, and a packaging product using said layered film.
As a result of extensive investigations, the present inventors have found that the above-described object can be attained by stacking a specific resin composition layer and a high-density polyethylene layer. The present invention has been accomplished based on this finding.
More specifically, the layered film of the present invention comprises at least two layers of a resin composition layer [layer (A)] comprising (a) from 60 to 90% by weight of a linear low-density polyethylene produced using a single site catalyst and (b) from 40 to 10% by weight of a polybutene-1, and a high-density polyethylene layer [layer (B)] comprising (c) a high-density polyethylene having a density of 0.950 to 0.970 (g/cm3).
The linear low-density polyethylene of the layer (A) has a density of 0.890 to 0.935 (g/cm3) and a melt flow rate of 2 to 20 (g/10 min).
The high-density polyethylene (c) of the layer (B) has a melt flow rate of 1 to 15 (g/10 min).
The layered film is produced by forming a film at an extrusion temperature of 160 to 250xc2x0 C. and cooling the film at a cooling temperature of 40 to 80xc2x0 C.
The packaging product of the present invention comprises sealant layers, wherein one sealant layer is a layer (A) of a layered film comprising at least two layers of a resin composition layer [layer (A)] comprising (a) from 60 to 90% by weight of a linear low-density polyethylene produced using a single site catalyst and (b) from 40 to 10% by weight of a polybutene-1, and a high-density polyethylene layer [layer (B)] comprising (c) a high-density polyethylene having a density of 0.950 to 0.970 (g/cm3).
In the packaging product of the present invention, one sealant layer is the layer (A) of said layered film comprising at least two layers of the layer (A) and the layer (B) and another sealant layer is a linear low-density polyethylene layer [layer (C)] comprising (d) a linear low-density polyethylene, which is produced using a single site catalyst, having a density of 0.890 to 0.925 (g/cm3) and a melt flow rate of 2 to 10 (g/10 min).
In the packaging product of the present invention, one sealant layer is the layer (A) of said layered film comprising at least two layers of the layer (A) and the layer (B), and another sealant layer is a layer (C) of a layered film comprising at least two layers of a linear low-density polyethylene layer [layer (C)] comprising (d) a linear low-density polyethylene, which is produced using a single site catalyst, having a density of 0.890 to 0.925 (g/cm3) and a melt flow rate of 2 to 10 (g/10 min), and a high-density polyethylene layer [layer (D)] comprising (e) a high-density polyethylene having a density of 0.950 to 0.970 (g/cm3).
In the packaging product of the present invention, the layer (A) has a thickness of 3 to 15 xcexcm.
In the packaging product of the present invention, the layered film comprising at least two layers of the layer (A) and the layer (B) is produced by forming a film at an extrusion temperature of 160 to 250xc2x0 C. and cooling the film at a cooling temperature of 40 to 80xc2x0 C.
The layered film of the present invention comprises at least two layers of a linear low-density polyethylene layer [layer (C)] comprising (d) a linear low-density polyethylene, which is produced using a single site catalyst, having a density of 0.890 to 0.925 (g/cm3) and a melt flow rate of 2 to 10 (g/10 min), and a high-density polyethylene layer [layer (D)] comprising (e) a high-density polyethylene having a density of 0.950 to 0.970 (g/cm3).
The layered film of the present invention is produced by forming a film at an extrusion temperature of 160 to 250xc2x0 C. and cooling the film at a cooling temperature of 40 to 80xc2x0 C.
The present invention is described in detail below.
In the present invention, out of the resin compositions constituting the layer (A), the linear low-density polyethylene (hereinafter referred to as xe2x80x9cSLLDxe2x80x9d) produced using a single site catalyst as the component (a) is obtained using a metallocene-base polymerization catalyst having a plurality of ligands and includes a linear low-density polyethylene having excellent low-temperature heat sealability and high transparency.
The SLLD means a copolymer of an ethylene with at least one member selected from xcex1-olefins having from 3 to 20 carbon atoms.
The xcex1-olefin having from 3 to 20 carbon atoms is preferably an xcex1-olefin having from 3 to 12 carbon atoms and specific examples thereof include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene and 1-dodecene. The content of the xcex1-olefin having from 3 to 20 carbon atoms occupying in the copolymer is generally 30 mol % or less, preferably from 2 to 20 mol %.
The SLLD for use in the present invention preferably has a density (measured according to JIS K 7112 D Method) of 0.890 to 0.935 (g/cm3), more preferably from 0.900 to 0.933 (g/cm3), still more preferably from 0.910 to 0.931 (g/cm3).
If the density is less than 0.890 (g/cm3), the heat seal strength may be too strong, whereas if it exceeds 0.935 (g/cm3), a feathering phenomenon is liable to occur.
The melt flow rate (hereinafter referred to as xe2x80x9cMFRxe2x80x9d) is preferably from 2 to 20 (g/10 min), more preferably from 6 to 18 (g/10 min), and still more preferably from 7 to 17 (g/10 min).
If the MFR is less than 2 (g/10 min), the heat seal strength is too strong and the clouding property tends to be inferior. On the other hand, if the MFR exceeds 20 (g/10 min), the compatibility with polybutene is poor, a feathering phenomenon may be generated or the clouding property tends to be inferior. Moreover, the MFR is measured according to JIS K 7210 Test Condition 4 at a temperature of 190xc2x0 C. under a load of 21.18 N.
The polybutene-1 (hereinafter referred to as a xe2x80x9cPBxe2x80x9d) as the component (b) is obtained by the polymerization starting from a butene-1 monomer and is the same polyolefin as polyethylene and polypropylene. In general, the PB has a high molecular weight and a high isotacticity. For the polymerization, a polymerization method using a Ziegler-Natta catalyst and a butene-1 as a solvent, or a solution polymerization method using a hydrocarbon-base solvent such as hexane and heptane, is used.
The PB is known as a polymer having rubber elasticity because it has a second order transition point lower than that of polypropylene and therefore, the flexural modulus thereof at room temperature or a low temperature is higher than that of polypropylene (see, D. G. Natta et. al., J. Polymer Sci., Vol. 25, p. 119 (1957)).
As compared with polyethylene or polypropylene, the PB is excellent in the mechanical properties such as tensile strength, impact strength and tear strength, and therefore, is used as a pipe starting material, a tube or a modifier.
In the field of film, the PB is used by blending it with another resin so as to impart low temperature heat sealability or easy peelability.
The properties and uses of the PB are described in detail, for example, in Saishin Laminate Kako Binran (Newest Lamination Processing Handbook), pp. 861-866 (1989), Kako Gijutsu Kenkyu Kai, and I. D. Rubin, Poly(1-Butene)xe2x80x94its Preparation and Properties, Gordon and Breach Science Publishers, Inc., New York (1968).
The PB for use in the present invention preferably has an MFR of 0.5 to 15 (g/10 min) according to ASTM D1238E, more preferably from 0.8 to 12 (g/10 min), and still more preferably from 1 to 10 (g/10 min). If the MFR is less than 0.5 (g/10 min), the seal strength may be too high, whereas if it exceeds 15 (g/10 mm), a feathering phenomenon may occur upon peeling the sealed portion or the clouding property may be inferior at the time of peeling.
The melting point of PB, measured by a method using a differential scanning calorimeter (DSC), is preferably 100 to 140xc2x0 C. If the melting point is less than 100xc2x0 C., a feathering phenomenon may occur in the portion where the sealed portion is peeled, or the clouding property is likely to be inferior at the time of peeling, whereas if it exceeds 140xc2x0 C., the heat seal strength and the clouding property tend to be inferior.
The PB is available, for example, under the trade name of xe2x80x9cBEAULONxe2x80x9d from Shell Chemical and Mitsui Chemicals, and these PBs can be suitably used.
The blend ratio between the component (a) and the component (b) constituting the layer (A) is preferably such that the SLLD is from 60 to 90% by weight and the PB is from 40 to 10% by weight.
If the SLLD is less than 60% by weight, reduction may be caused in the water vapor barrier property, the seal strength and the clouding property, and also, a feathering phenomenon is disadvantageously liable to occur at the time of peeling.
On the other hand, if it exceeds 90% by weight, the clouding property deteriorates or at the heat sealing, sealing occurs in the periphery of the seal portion to impair the appearance of the packaging product or discourage the taking out of the contents.
The blend ratio is preferably such that the SLLD is from 65 to 85% by weight and the PB is from 35 to 15% by weight, more preferably the SLLD is from 67 to 82% by weight and the PB is from 32 to 18% by weight.
The high-density polyethylene (c) (hereinafter referred to as xe2x80x9cHDPExe2x80x9d) constituting the layer (B) preferably has a density of 0.950 to 0.970 (g/cm3), more preferably from 0.952 to 0.965 (g/cm3), and still more preferably from 0.953 to 0.962 (g/cm3). If the density is less than 0.950 (g/cm3), the water vapor barrier property decreases, or the clouding property at the time of peeling tends to be inferior, whereas if it exceeds 0.970 (g/cm3), the low temperature heat sealability or clouding property tends to be impaired.
The MFR of the high-density polyethylene (c) is preferably from 1 to 15 (g/10 min), more preferably from 2 to 13 (g/10 min), and still more preferably from 3 to 12 (g/10 min). If the MFR is less than 1 (g/10 min), the low temperature heat sealability and the clouding property tend to be inferior, whereas if it exceeds 15 (g/10 min), the film readily tears in the longitudinal direction or a feathering phenomenon may occur at the time of peeling.
For laminating the layer (A) and the layer (B), a known forming method may be used. Examples thereof include an extrusion lamination method, a co-extrusion inflation method and a co-extrusion T-die casting method.
In the case of obtaining the layered film (hereinafter referred to as xe2x80x9clayered film Ixe2x80x9d) comprising at least two layers of the layer (A) and the layer (B) of the present invention by a co-extrusion method, the film is preferably formed at an extrusion temperature of 160 to 250xc2x0 C. and cooled at a cooling temperature of 40 to 80xc2x0 C., so that good water vapor barrier property and excellent clouding property can be obtained.
For satisfying the object of the present invention, the layered film I of the present invention has a thickness of 20 to 70 xcexcm, preferably from 20 to 60 xcexcm, and more preferably from 25 to 50 xcexcm.
Examples of the layer structure include (A)/(B), (A)/(B)/(A) and (A)/(B)/other layer.
The thickness of the layer (A) is suitably from 3 to 15 xcexcm by taking account of the invasion of water vapor from the end surface of the packaging product produced.
The thickness ratio between the layer (A) and the layer (B) is suitably layer (A):layer (B)=0.05 to 0.3:0.95 to 0.7. The thickness ratio is preferably layer (A):layer (B)=0.07 to 0.25:0.93 to 0.75, and more preferably 0.1 to 0.2:0.9 to 0.8.
If the thickness ratio of the layer (A) is less than 0.05, a location is generated where both of the layers (B) are partially heat-sealed when heat-sealing is applied and this may cause problems such that the heat seal strength elevates or on opening, the layered film is cut at the heat seal end part, and as a result, the contents cannot be easily taken out. On the other hand, if the thickness ratio of the layer (A) exceeds 0.3, feathering takes place or the water vapor barrier property of the packaging product may decrease.
In the packaging product of the present invention, a layered film comprising at least 2 layers of layer (A) and layer (B) is used, with layer (A) as the sealant layer.
In peeling the packaging product comprising the above-described layer (A) (resin composition layer) as a sealant layer, cohesive peeling due to cohesive failure is generated inside the resin composition layer comprising SLLD and PB each in specific amount, whereby excellent openability and high clouding property are revealed.
Although the reason is not clearly known, excellent clouding property as one object of the packaging product of the present invention is presumed attributable to the fact that the PB constituting the resin composition layer has a higher molecular weight and a higher cohesive energy than SLLD and therefore, when the packaging product is peeled, fine voids are generated on the interface between PB and SLLD.
In the packaging product of the present invention, a layer comprising HDPE must be stacked on the above-described sealant layer (a resin composition layer comprising SLLD and PB each in a specific amount).
This is because unless a layer comprising HDPE is stacked on the sealant layer, reduction in the water vapor barrier property or poor seal strength stability may result and in an extreme case, the periphery of the heat seal portion melts to cause bonding and the contents of the packaging product cannot be easily taken out.
Accordingly, the packaging product having excellent openability, good clouding property, high water vapor barrier property and superior seal strength stability, which is the object of the present invention, can be first obtained by using a layered film where the layer comprising HDPE is stacked on the sealant layer (a resin composition layer comprising SLLD and PB each in a specific amount).
In the packaging product of the present invention, it is also possible that one sealant layer is a resin composition layer comprising SLLD and PB each in a specific amount and another sealant layer is a layer comprising SLLD.
A suitable example of the layered film having such a layer comprising SLLD is a layered film (hereinafter referred to as xe2x80x9clayered film IIxe2x80x9d) comprising at least two layers of a linear low-density polyethylene layer [layer (C)] comprising (d) a linear low-density polyethylene, which is produced using a single site catalyst, having a density of 0.890 to 0.925 (g/cm3) and an MFR of 2 to 10 (g/10 min), and a high-density polyethylene layer [layer (D)] comprising a high-density polyethylene having a density of 0.950 to 0.970 (g/cm3), where the layer (C) of the layered film II is the sealant layer.
The linear low-density polyethylene (d) and the high-density polyethylene (e) used in the layered film II may be the same as those used in the layer (A) and the layer (B) of the layered film I, respectively.
For laminating the layer (C) and the layer (D), a known forming method may be used. Examples thereof include an extrusion, lamination method, a co-extrusion inflation method and a co-extrusion T-die casting method.
In the case of obtaining the layered film II of the present invention by a co-extrusion method, the film is preferably formed at an extrusion temperature of 160 to 250xc2x0 C. and cooled at a cooling temperature of 50 to 80xc2x0 C., so that good water vapor barrier property and excellent clouding property can be obtained.
For satisfying the object of the present invention, the layered film II comprising the layer (C) and the layer (D) of the present invention has a thickness of 20 to 70 xcexcm, preferably from 20 to 60 xcexcm, more preferably from 25 to 50 xcexcm.
Examples of the layer structure include (C)/(D), (C)/(D)/(C) and (C)/(D)/other layer.
The thickness of the layer (C) is suitably from 3 to 15 xcexcm by taking account of the invasion of water vapor from the end surface of the packaging product produced.
The thickness ratio between the layer (C) and the layer (D) is suitably layer (C):layer (D)=0.05 to 0.3:0.95 to 0.7. The thickness ratio is preferably layer (C):layer (D)=0.07 to 0.25:0.93 to 0.75, and more preferably 0.1 to 0.2:0.9 to 0.8.
If the thickness ratio of the layer (C) is less than 0.05, a location is generated where both the layers (D) are partially heat-sealed when heat-sealing is applied and this may cause problems such that the heat seal strength elevates or on opening, the layered film is cut at the heat seal end part, and as a result, the contents cannot be easily taken out.
On the other hand, if the thickness ratio of the layer (C) exceeds 0.3, feathering takes place or the water vapor barrier property of the packaging product may decrease.
As described above, in the packaging product of the present invention, it may also be possible that one sealant layer is a resin composition layer, which is stacked on the HDPE, comprising SLLD and PB each in a specific amount and another sealant layer is a layer comprising SLLD.
More specifically, the packaging product of the present invention may have a construction such that one sealant layer is the layer (A) of the layered film I and another sealant layer is the layer (C) of the layered film II.
In other words, the object of the present invention can be attained as long as at least one sealant layer of the packaging product of the present invention is the layer (A) comprising SLLD and PB of the layered film I. The other sealant layer is preferably the SLLD but may not contain PB.
The constituent materials in each layer constituting the present invention may be blended with an appropriate amount of other additives commonly used for the thermoplastic resin (for example, antioxidant, weatherability stabilizer, antistatic agent, lubricant, blocking inhibitor, antifogging agent, dye, pigment, oil, wax, filler) or other thermoplastic resins within the range of not impairing the object of the present invention.
Examples of the additives include an antioxidant such as 2,5-di-tert-butylhydroquinone, 2,6-di-tert-butyl-p-cresol, 4,4xe2x80x2-thiobis(6-tert-butylphenol), 2,2-methylene-bis(4-methyl-6-tert-butylphenol), octadecyl-3-(3xe2x80x2,5xe2x80x2-di-tert-butyl-1xe2x80x2-hydroxyphenyl)propionate and 4,4xe2x80x2-thiobis(6-butylphenol), an ultraviolet absorbent such as ethyl-2-cyano-3,3-diphenylacrylate, 2-(2xe2x80x2-hydroxy-5-methylphenyl)-benzotriazole and 2-hydroxy-4-octoxybenzophenone, a plasticizer such as dimethyl phthalate, diethyl phthalate, wax, liquid paraffin and phosphoric acid ester, an antistatic agent such as pentaerythritol monostearate, sorbitan monopalmitate, sulfated oleic acid, polyethylene oxide and carbon wax, a lubricant such as ethylenebisstearamide and butyl stearate, a coloring agent such as carbon black, phthalocyanine, quinacridone, indoline, azo-type pigment, titanium oxide and red iron oxide, a filler such as glass fiber, asbestos, mica, wollastonite, calcium silicate, aluminum silicate and calcium carbonate, and an antiblocking agent such as silica type antiblocking agent, silicone type antiblocking agent, zeolite type antiblocking agent, talc, and polymethylmethacrylate (PMMA) particles. Many other polymer compounds may also be blended to the extent of not inhibiting the operational effect of the present invention.
The method for blending the resin composition of the present invention is not particularly limited and a known method may be used. For example, a method of mixing respective components by a mixer such as mixing roll, Banbury mixer, Henschel mixer, tumbler or ribbon blender and then pelletizing the mixture using an extruder, or a method of directly dry-blending and forming the components may be used.
Other polyolefin-base resin layers may also be further laminated within the range of not impairing the object of the present invention.
The layered film of the present invention can be made into a formed article by a known extrusion laminating method using a forming machine. Also, by using a known dry-lamination machine, other materials may be laminated before use, to provide a gas barrier layer of aluminum foil, metallized film, silicon oxide-deposited film, vinylidene chloride resin or ethylene-vinyl acetate copolymer saponified product, a polyester resin layer, a polyamide resin layer or a polycarbonate resin layer.